Analysis of 2 Major Factors of MLCC Leakage

Although the function of MLCC is simple, because it is widely used in electronic products such as smart phones, once it fails, it will cause circuit failure, abnormal function, and even cause product combustion, explosion and other safety issues. Its failure mode has to be subject to quality inspection and other related engineers. attention.

Among the various failure modes, capacitor leakage (low insulation resistance) is the most common type of failure. The main reasons can be divided into internal factors in the manufacturing process and external factors in the production process.

1. Intrinsic factors

1. Void

The foreign matter inside the capacitor volatilizes away during the sintering process to form a cavity. Voids can cause short circuits between electrodes and potential electrical failures. If the voids are larger, not only will the IR be reduced, but the effective capacitance will also be reduced. When the power is turned on, it is possible that the cavities may locally generate heat due to leakage, which reduces the insulation performance of the ceramic medium and aggravates the leakage, resulting in cracks, explosions, burning and other phenomena.

2. Crack

Sintering cracks are generally caused by rapid cooling during the sintering process and appear in the vertical direction of the electrode edge.

3. Delamination

Delamination is often caused by poor lamination or insufficient debinding and sintering after stacking. Air is mixed between layers and external impurities cause jagged lateral cracks. It may also be caused by mismatched thermal expansion after mixing different materials.

2. External factors

1. Thermal shock

Thermal shock mainly occurs during wave soldering. The temperature changes sharply, causing cracks between the electrodes inside the capacitor. Generally, it is found through measurement. Observation after grinding, usually small cracks, which need to be confirmed with a magnifying glass. In a few cases, they will be visible to the naked eye. Cracks.

In this case, it is recommended to use reflow soldering, or to slow down the temperature change during wave soldering (no more than 4~5℃/s), and control the temperature below 60℃ before cleaning the panel.

2. External mechanical stress

Because the main component of MLCC is ceramics, in the process of placing components, sub-boards, screwing, etc., it is possible that excessive mechanical stress will cause the capacitor to be crushed and ruptured, resulting in potential leakage failure. The cracks at this time are generally oblique, cracking from the junction of the terminal and the ceramic body.

3. Solder migration

Soldering in a high-humidity environment may cause the solder on both ends of the capacitor to migrate, which may cause leakage and short circuit when connected together.